Type-2 diabetes is a chronic metabolic disorder due to a combination of insufficient pancreatic insulin production and/or insulin resistance (IR). The most prominent clinical feature is hyperglycemia characterized by an abnormally high level of glucose in the blood. Hypertension, hyperlipidemia, hyperinsulinemia, and atherosclerosis are often associated with diabetes (Dey et al, 2002, Altern. Med. Rev. 7, 45-58). Hyperglycemia can cause oxidative stress which is ultimately responsible for the development of chronic diabetes complications (Ziegler et al, 2004, Diabetes Care 27, 2178-83; Evans et al, 2002, Endoc. Rev. 23, 599-622). Type-2 diabetes usually begins as IR, and obesity is a known high risk factor for developing IR (Ferrannini et al, 1997, J. Clin. Invest. 100, 1166-73). The main biochemical markers of IR include glucose intolerance, dyslipidaemia, and hyperinsulinaemia (Peter et al, 2003, J. Clin. Pharm. Ther. 28, 167-74). Therefore, regulation of blood glucose, control of bodyweight and body fat, and attenuation of oxidative stress should be targets in the treatment of Type-2 diabetes.
Rosemary leaf consists of Rosmarinus officinalis L. (Family Lamiaceae). It is a culinary spice often used to adjust flavor in cooking and in tea infusion. In folk medicine, Rosemary is used as a choleretic, a diuretic, an antispasmodic, a hair-growth stimulator, to treat gastrointestinal symptoms, as well as other uses (Bruneton, J., Pharmaconosy, Phytochemistry, Medicinal Plants, Lavoisier Publishing, Paris, 1995, pp 220; Duke, J., Handbook of Medicinal Herbs, CRC Press, Boca Raton, 1985, pp 412-413; al-Sereiti et al, 1999, Indian J. Exp. Biol. 37, 124-30). Rosemary is well-known as a natural antioxidant and widely applied in food conservation (Etter 2004, J. Herbs, Spices, Med. Plants, 11, 121-59; Suhaj 2006, J. Food Compos. Anal. 19, 531-7). Such antioxidant properties are also important to human health since overproduction of free radicals in living organisms can damage cellular lipids, proteins, or DNA, which has been implicated in a number of human diseases including diabetes as well as in the aging process (Valko et al 2007, Int. J. Biochem. Cell Biol. 39, 44-84).
Reduction in oxidative status is characteristic of patients having either Type-1 or Type-2 diabetes. This condition in diabetics increases lipid peroxidation and glycosilation of proteins, which leads to complications such as retinopathy, nephropathy, and coronary heart disease. Therefore, supplementation with dietary antioxidants may help to counteract the oxidative stress, and prevent the development of these negative conditions (Al-Azzawie et al, 2006, Life Sci. 78, 1371-7).
Several techniques have been developed to determine the antioxidant power of foods products, vegetal extracts, or pure molecules. These methods have been developed by starting from various principles which can be divided into two large categories of techniques based on major mechanisms that intervene in the stabilization of pro-oxidant species by antioxidants. The first method is based on hydrogen transfer from the antioxidant to the oxidant. The second method is based on electron transfer from the antioxidant to the oxidant. The methods based on hydrogen atom transfer measure the capacity of an antioxidant to trap free radicals by giving them a hydrogen atom. The most widely used is the Oxygen Radical Absorbance Capacity (ORAC) method, which measures the capacity of an antioxidant to inhibit oxidants induced by the peroxyl radical and reflects the inhibition induced by the antioxidant in the stages of initiation and/or propagation of oxidation (Cao et al, 1993, Free Radic. Biol. Med., 14, 303-311). The methods based on electron transfer determine the capacity of an antioxidant to transfer an electron from the antioxidant to the oxidant to reduce the oxidant. One of the most well known of these techniques is the Ferric Reducing/Antioxidant Power (FRAP) method, initially developed to measure the reduction power of plasma. It was later adapted and used for foodstuffs, plants and extracts. Its principle relies on the antioxidant's capacity to reduce Iron III to Iron II in an acidic environment (Pulido et al, 2000, J. Agric. Food Chem., 48, 3396-402).
The oxidation of low-density lipoprotein (LDL) is accepted as an important initial step in the development of atherosclerosis. Indeed, oxidized LDL might be taken up by macrophages to form foam cells, which will combine with leukocytes to become a fatty streak and, later, a fibrous plaque that will protrude into the arterial lumen. If the fibrous plaque ruptures, the thrombi released may occlude vessels and be responsible for adverse coronary syndromes. Recent reports suggest that Rosemary may protect against cardiovascular disease (CVD) (Fuhrman et al, 2000, Antioxid. Redox. Signal., 2, 491-506; Hsieh et al, 2007, J. Agric. Food Chem., 55, 2884-91).
Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that control many cellular and metabolic processes. These proteins are ligand-activated transcription factors and three isotypes called PPARα, PPARδ and PPARγ have been identified in lower vertebrates and mammals. PPARγ is expressed in the liver, fat, and muscle. The activation of PPARγ increases the transcription of enzymes involved in primary metabolism, leading to lower blood levels of fatty acids and glucose (Evans et al, 2004, Nat. Med., 10, 355-61; Rosen et al 2000, Genes Dev., 14, 1293-1307). PPARγ represents the major target for the glitazone type of drugs currently being used clinically for the treatment of type-2 diabetes. Carnosic acid and carnosol from rosemary and sage have been demonstrated to be activators of the human PPARγ (Rau et al 2006, Planta Med., 72, 881-887).
A major component of dietary fat is triglyceride, or neutral lipid. A triglyceride molecule cannot be directly absorbed across the intestinal mucosa; rather it must be digested into a 2-monoglyceride and two free fatty acids. The enzyme that performs this hydrolysis is pancreatic lipase, which plays an important role in lipid digestion. Orlistat, a strong pancreatic lipase inhibitor, is clinically used for controlling obesity in humans by reducing the amount of fat absorbed from the dietary intake (Scheen et al 1999, Int. J. Obes., 23, Suppl 1, 47-53; Hvizdos et al 1999, Drugs, 58, 743-760; Krempf et al, 2003, Int. J. Obes. Relat Metab. Disord., 27, 591-7).
It was found that methanol extract of sage, carnosic acid, and its derivatives had the capacity to inhibit pancreatic lipase (Ninomiya et al, 2004, Bioorg. Med. Chem. Lett., 14, 1943-6). Research showed that carnosic acid and carnosol substantially inhibited pancreatic lipase activity. Carnosic acid significantly inhibited triglyceride elevation in olive oil-loaded mice at doses of 5-20 mg/kg. Furthermore, carnosic acid (20 mg/kg/day) reduced the gain of body weight and the accumulation of epididymal fat weight after 14 days in mice fed a high fat diet.
The hypoglycemic effect of R. officinalis was first reported in 1997, in which the boiling water extract of the leaf of Rosemary was infused into normoglycemic and alloxan-induced hyperglycemic mice, and plasma glucose level was then measured. It was found that the glucose levels in both groups were significantly lower than in the control group (Erenmemisoglu et al, 1997, Pharmazie, 52, 645-6). The effect of 50% ethanol extract of Rosemary on the elevation of plasma glucose levels in the streptozotocin (STZ)-induced diabetic mice was examined. It was shown that Rosemary extract inhibited intestinal α-glucosidase activity to reduce carbohydrate digestion and absorption in mice, significantly suppressing an increase in plasma glucose levels after oral administration of maltose or sucrose. The active compound was identified as the flavonoid, luteolin (Koga et al, 2006, J. Food Sci., 71, S507-12). In a recent report, the hypoglycemic effect of the ethanolic extract from the leaves of Rosemary was observed in normoglycaemic and glucose-hyperglycaemic rabbits. In a study of alloxan-induced diabetic rabbits, the extract significantly lowered blood glucose level and increased serum insulin concentration. According to the authors, the antidiabetogenic effect of the rosemary extract was due to its potent antioxidant properties (Bakirel et al, 2008, J. Ethnopharmacol., 116, 64-73).